CALCUTTA, India (AP) _ Mother Teresa has agreed to undergo an angiogram _ a delicate, invasive procedure to check on the functioning of her arteries.

Doctors said Tuesday that Mother Teresa had been reluctant to undergo the test, but they considered it a necessary part of her treatment.

A date for the angiogram had not been set. Doctors said she may have to be moved to a more sophisticated hospital in Calcutta for the procedure.

The 86-year-old Roman Catholic nun has been in intensive care since Friday, when one of the four chambers of her heart failed to perform properly. A Woodlands Nursing Home statement late Monday described her condition as ``unchanged.''

``She is not out of danger,'' said S.K. Sen, the hospital's medical director.

Mother Teresa's medical team was considering performing an angiogram to determine whether an angioplasty is necessary, Sen said.

An angiogram involves puncturing an artery, usually in the groin, and inserting a tube up into the chest arteries that feed the heart. X-ray dye is then injected into the arteries and pictures are taken.

That could be followed up by an angioplasty, in which the arteries are dilated to increase blood flow. Mother Teresa has undergone two angioplasties in the past.

Doctors often are reluctant to recommend such invasive tests for frail, elderly patients because there is a risk of infection.

Mother Teresa, recipient of the 1979 Nobel Peace Prize, has suffered two heart attacks since 1983 and has a pacemaker. So far this year, she has been hospitalized four times _ twice with heart problems and twice with injuries sustained during falls.

Over the weekend, she suffered chest pain and breathing problems.

About 100 nuns at the Calcutta headquarters of the order she founded 50 years ago, Missionaries of Charity, prayed for her recovery at their regular morning Mass on Monday.

It was unclear how her latest health problems will affect plans to elect a successor as head of the order. The nuns were to hold elections within the next few months. The order's constitutional requires a vote every six years.

In 1990, Mother Teresa announced that she wanted to retire, and her name was not on the ballot. She reluctantly agreed to stay on after all the sisters wrote her name in anyway.

Sister Priscilla Lewis, a senior administrator of the order, was quoted over the weekend as saying the election will go ahead as planned ``if Mother's health and other factors permit.''

The Missionaries of Charity operates 517 centers around the world, including 169 in India. Aides have taken over more and more day-to-day responsibilities since Mother Teresa's health began to decline.